Skin Cancer in Dogs

small dog in the sun

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Despite the fact that dogs are typically covered in fur, they can still develop skin cancer. While it can be a factor, sun exposure isn't the only cause of skin cancer in dogs. A few different forms of skin cancer can unfortunately affect dogs and it's important for dog owners to recognize the potential signs of the disease in order to treat it as quickly as possible.

What is Skin Cancer in Dogs?

Cancer develops when abnormal cells grow in a dog. These abnormal cells grow and sometimes form tumors in the skin of a dog. These tumors can spread and some forms of skin cancer can be fatal which is why it is so important to identify and treat them as soon as they are found.

Signs of Skin Cancer in Dogs

  • A lump on the skin
  • A bleeding or oozing area on the skin
  • Dog excessively itches or licks at one area on the skin

The most obvious sign that a dog may have skin cancer is a lump or growth on the skin. Small lumps may not be as easily seen as larger lumps, especially if they are on a furry part of a dog. But not all lumps are cancerous on dogs. Some lumps are simply pimples, skin tags, nipples, warts, or consist of fat and do not necessarily pose a health concern to a dog.

Sometimes cancerous masses or skin lesions will bleed or ooze and not heal like a typical wound would. These parts of the skin may have this difficulty healing because they are filled with cancerous cells. They may also be irritating to a dog which could cause it to lick or itch at this area excessively, causing more trauma and subsequent bleeding.

Types of Skin Cancer in Dogs

  • Squamous Cell Carcinoma: This type of cancer can be caused by sun exposure but it may be a result of other causes that are not fully understood by scientists. Squamous cell carcinomas can spread to the surrounding tissues but do not typically invade the lymphnodes or internal organs.
  • Malignant Melanoma: This type of cancer also occurs in humans, but in dogs, it affects the melanocytes in the skin which are responsible for creating the pigment or colored areas. These tumors usually occur on parts of a dog's body that do not have fur, such as the mouth, and can be a variety of colors. Malignant melanoma can spread very quickly to other parts of the body including internal organs.
  • Melanocytomas: Also a type of melanoma, these tumors are usually benign, which means they do not spread. Melanocytomas usually occur on furry parts of a dog's body.
  • Mast Cell Tumors: The most commonly diagnosed type of skin cancer in dogs, mast cell tumors are made up of mast cells. Often abbreviated as MCT's, they can look similar to a fatty mass but can also spread very quickly or be very small. There are varying grades of mast cell tumors that carry different levels of risk to a dog. Lower grades of mast cell tumors are not as concerning as higher grades which are known to be aggressive and spread in the body.
    • Grade 1 Mast Cell Tumor: This is considered a low-grade mast cell tumor and if the entire tumor is surgically removed it is often curable.
    • Grade 2 Mast Cell Tumor: This grade of MCT is more serious than a grade 1. It often spreads to the local lymphnodes but not usually to the rest of the body. This can be a confusing grade of MCT because it will also be assigned something called a mitotic index which will give more insight into how quickly the cancer cells are multiplying in the tumor. Low mitotic index grade 2 MCT's are often curable if they are completely removed with surgery as soon as they are discovered but grade 2 MCT's with a high mitotic index may need chemotherapy or additional treatment after surgery.
    • Grade 3 Mast Cell Tumor: The most concerning level of MCT, a grade 3 spreads quickly to other parts of the body including internal organs. There is aggressive treatment but most of these tumors are not able to be cured or completely removed.
    Skin cancer on a dog
    A lump is the most obvious sign of skin cancer on a dog. Getty Images/Elen11

    Causes and Risk Factors of Skin Cancer in Dogs

    Just like in people, all of the causes of skin cancer in dogs are not completely understood but there are some specific things scientists know contribute to the likelihood of a dog developing it.

    • Sun Exposure: Areas of skin that are not protected by thick fur are more likely to be develop skin cancer, especially if that skin is a light color. These areas may be completely hairless or just have a short or thin layer of fur.
    • Specific Dog Breeds: Vizslas, all sizes of Schnauzers, Doberman Pinschers, Airedale Terriers, Bay Retrievers, Scottish Terriers, Keeshonds, Labrador Retrievers, Bassett Hounds, Collies, Dalmatians, Bull Terriers, Beagles, Boxers, Pugs, and Boston Terriers may all be more likely to develop different types of skin cancers than other breeds.
    • Black Dogs: Dogs of this fur color seem to be more likely to develop skin cancers on their feet or toes.
    • Adult and Senior Dogs: As dogs mature, they seem to develop cancer at higher rates than younger dogs.
    • Excessive Licking or Chewing: If a dog licks or chews excessively at one area on its skin it may elevate the risk of developing skin cancer in that area due to the inflammation and irritation caused.

    Diagnosing Skin Cancer in Dogs

    A veterinarian will do a complete physical examination of your dog to look for abnormal skin growths or lesions. If one is discovered, they may recommend surgical removal, a biopsy, or the aspiration of cells in order to diagnose whether or not it is skin cancer. All of these tests will observe the cells under a microscope to see if they are normal or cancerous. The recommendations for diagnostic tests may vary depending on the location, size, feel, and age of the growth.

    Treatment of Skin Cancer in Dogs

    Some skin cancers may be able to be completely surgically removed but others may have no cure. Surgical removal of a lump will give a dog the best chance at a positive outcome but sometimes chemotherapy, radiation, steroids, and other treatments will be necessary to prolong a good quality of life for a dog with skin cancer. Treatment will vary greatly on the type of skin cancer a dog is diagnosed with.

    How to Prevent Skin Cancer in Dogs

    There is unfortunately no good way to prevent all types of skin cancer. For dogs with little or no fur, limiting sun exposure may help decrease the likelihood of developing melanomas but the root cause of cancer cells forming inside the body is not well understood. Despite this, many people give antioxidants to their pets since they may help scavenge free radicals and therefore decrease the development of cancerous cells but there is no guarantee that this will prevent anything. Decreasing excessive inflammation may also help to discourage cancerous cells to proliferate.